Replace "edX Studio" with "{studio_name}"

For theming and internationalization
Refactor sock HTML to have text in Mako template
Use STUDIO_SHORT_NAME for Studio

STUDIO_NAME = "edX Studio"
STUDIO_SHORT_NAME = "Studio"
Add settings comment about STUDIO_NAME and STUDIO_SHORT_NAME
Merge pull request #6309 from edx/db/edx-studio-as-format-string

Replace "edX Studio" with "{studio_name}"